This invention relates to electrical switches, and more particularly, to a precision, multiposition, non snap acting, human digit operated switch.
Moving boats, off road vehicles, helicopters, airplanes, etc. encounter sudden and sometimes unexpected "G"forces when in operation. Human operators of these moving devices may be called upon to perform electrical switching control operations during encounter with these "G"forces in addition to operations during normal "G"force conditions. The switches for these switching operations are often associated with a manual grip mechanism which provides multiple control functions with switch actuation occuring simultaneously with other control operations such as movement of the entire grip in a steering operation for a vehicle or boat or a joystick for an airplane.
Thumb or finger operated snap acting switches have usually been heretofore used in such applications for their known good electrical characteristics in positive switching. However, in addition to being physically larger, the heretofore used snap switches, to impart needed contact pressures and other required characteristics have other undesirable characteristics. The normal "snap action"operation of these switches requires changing input forces and/or sudden releases of forces, both often in the range of two to five pounds usually associated with some overcentering mechanism and internal spring, the input forces being provided by the thumb or finger and the reaction to these forces being taken up either in the grip, or in the operating thumb or finger, or both. When operated during a sudden or unexpected high "G"force environment, say 8 to 50 "Gs", these input and release forces can be greatly magnified. This may make actuating movement difficult or the sudden absence of needed input force at trip-point can sometimes cause unwanted movement of the grip mechanism by the operator, etc. Since the high "G"force encounters usually occur at dangerous times when control by the operator is ofen critical and precise controlled switch actuation by the operator is most needed, it can be seen that the elimination of the changing force characteristics involved in snap action switches is advantageous.
It is important that the switches be very stable and not self actuate from an "off"to an "on"position (or vice versa) when an aircraft, boat or vehicle is subjected to sudden shock that may produce transitory "G"force on the order of 50 "Gs". Thus the elimination of snap force characteristics can not be at sacrifice of stability under shock conditions or precision.
Further as vehicles and planes become more sophisticated, more and more control features are often packed into control grips whereby space is at a premium. Thus there is considerable need and demand for a more compact precision switch which may be successively actuated into a number of different positions. However, because human and vehicular safety may often be at stake, the compactness can not be obtained at the sacrifice of ruggedness, long actuating life, repeatable precision, stability under shock conditions, good electrical characteristics and good "feel".
The invention provides a non snap action, multiposition, rugged, sealed switch which is compact yet precise. Very small actuator travel and low actuation force is required to cause actuation of the movable contact from center off to engagement with various fixed contacts. The geometry of the movable parts of the switch translates the low travel movement into good movement of the movable contact toward, high unit pressure with, and wiping engagement with the fixed contact. This may be accomplished with very low input actuation force (typically in the vicinity of 16 oz.) and is easily supplied in all modes of actuation by a human thumb or finger.
The actuator is pivotally mounted on an internal array of switch casing pivot surfaces located in predetermined relation to mode locator slots formed above the pivot surfaces. The actuator is formed with a separate set of pivot surfaces for receiving the movable contact member which initially pivots from the center off position with the actuator member. After generally radial movement to engagement of the movable contact member with a fixed contact, and upon further movement of the actuator toward overtravel stop position, the movable contact pivots on the separate set of pivot surfaces on the actuator and on the fixed contact while maintaining solid wiping contact engagement. The configuration of the parts now introduces a general change in the direction of the movement of the movable contact which moves downwardly into engagement with an abutment means formed in the switch casing while maintaining engagement with the fixed contact. The abutment means has surfaces which constrains movement of the movable contact away from the fixed contact under certain conditions. The overtravel stop function is provided by side surfaces in the central switch opening which are engageable by the actuator. When the actuator is in full overtravel stop position, the actuator is pivotal about an additional point, namely the stop surface, and small movement of the actuator about this new additional pivot point could undesirably break electrical contact between the movable contact member and the fixed contact but for the abutment means in the switch casing.
The switch casing pivot surfaces and the separate actuator pivot surfaces for a four position "on"center "off"switch embodiment (but not other embodiments) may be formed in aligned square arrays along with square arrays of complimentary coacting parts on the actuator and on the contact member so that pivotal action about one side of switch casing pivot surfaces causes pivotal action about the opposite side of the square on the separate actuator surfaces. All embodiments provide precision double hinge like action in all modes while maintaining easy assembly orientation with each other and with the mode locator slots formed in the top of the casing.
A single biasing spring is required, one end engaging the movable contact member, the other the switch casing, to serve the multiple functions of returning all parts to center off position, maintain the movable contact member against the separate pivot means on the actuator, maintain the actuator in operable relation to the switch casing pivot surfaces, overpower inertial movement of the moving parts under conditions of shock and sudden high "G"forces, help impart repeatable precision movements, and in relatively low amperage usages, be a part of the common terminal path so as to reduce cost and aid in assembly operations. A flexible seal which permits complex movement of the actuator is provided so that dust and other contaminants can be kept from the moving parts.
The switch, while providing many varied good electrical and mechanical characteristics and functions in very small size, has long actuation life, is relatively easily made and assembled and has few parts.